-LRB- CNN -RRB- -- Zambian police rearrested two men this week on charges of engaging in homosexual acts `` against the order of nature , '' a rights group said .

James Mwansa and Philip Mubiana , both 21 , were arrested after neighbors reported them to the police , according to Amnesty International .

Authorities subjected them to anal examinations without their consent and forced them to confess , the human rights group said .

`` Anal examinations conducted to ` prove ' same-sex conduct are scientifically invalid , and if they were conducted without the men 's consent , contravene the absolute prohibition of torture and other cruel , inhuman and degrading treatment or punishment under international law , '' said Simeon Mawanza , an Amnesty researcher in Zambia .

It was the second detention for the two men in recent days , the group said . Last month , authorities arrested them , and later released them on bail on May 2 .

They were arrested again Monday and have been denied bail , according to Amnesty . Both have pleaded not guilty , and are being held at a jail in Kapiri Mposhi until their trial starts May 22 .

`` The arrest of the two men solely for their real or perceived sexual orientation amounts to discrimination and it is in violation of their rights to freedom of conscience , expression and privacy , '' Mawanza said .

Zambian officials were not immediately available for comment .

Homosexuality is illegal in Zambia and most African countries based on remnants of sodomy laws introduced during the British colonial era and perpetuated by cultural beliefs .

Punishments across the continent range from fines to years in prison .

Last year , a Cameroon appeals court upheld a three-year sentence against a man convicted of homosexuality for texting his male friend to say , `` I 'm very much in love with you . ''

South Africa -- one of the more progressive nations in the continent on the issue -- was the first African country to impose a constitutional ban on discrimination based on sexual orientation .

But sexual violence against lesbians has become so common in South Africa , the nation has coined the term `` corrective rape '' to describe it .

A handful of other nations issue a death penalty for consensual same-sex relations , including Saudi Arabia and Iran , according to the International Lesbian , Gay , Bisexual , Trans and Intersex Association .

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Authorities subject them to anal examinations without their consent , a rights group says

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Amnesty International : It was the second detention for the two men in recent days

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Homosexuality is illegal in most African countries